Effect Of Oxygen On Strength And Plasticity Of Zr-based Metallic Bulk Glasses

Bulk amorphous alloys?BMGs?are potential candidates for next-generation structural engineering materials due to their excellent range of properties such as high strength and hardness,high elastic limit and excellent corrosion resistance.However,due to the purity of the raw materials and the influence of the smelting process,the alloy will inevitably contain a certain amount of oxygen.Therefore,a correct understanding of the mechanism and law of oxygen is of great significance for the promotion and application of amorphous alloys in engineering practice.In this thesis,Zr-based amorphous alloy was prepared by copper mold suction casting method.The effect of oxygen on the amorphous forming ability,mechanical properties and reliability of Zr-based amorphous alloy was studied by systematic addition of oxygen.Six kinds of amorphous alloys(Zr_0.61Cu_0.25Al_0.12Ti_0.02)_100-xO_x?x=0.01,0.04,0.08,0.12,0.16,0.2,wt.%?were prepared by copper die casting method.The actual measured oxygen contents were 66,360,780,1100,1500 and 1900 ppm,respectively.When the oxygen content is lower than 360 ppm,the amorphous forming ability is maintained as the oxygen content is increased,and the critical dimension is significantly higher than 8 mm.When the oxygen content exceeds 360 ppm,the amorphous forming ability decreases drastically with the increase of oxygen content,the critical size is much less than 8 mm,and the critical dimension of the alloy drops below 2 mm at 1900 ppm oxygen content.When the oxygen content exceeds a certain oxygen content level,the?3 crystal phase precipitates in the Zr₆₁Cu₂₅Al₁₂Ti₂ alloy.As the oxygen content continues to increase,the?₃ crystal phase increases sharply,and is dispersed throughout the alloy.Oxygen promotes the growth of the?₃ crystal phase.effect.The glass transition temperature of Zr₆₁Cu₂₅Al₁₂Ti₂ alloy increases from 653 K to 670 K with the increase of oxygen content,and then decreases to 648 K.The crystallization temperature T_x1 is basically unchanged with the increase of oxygen content,and the temperature of the supercooled liquid region is constant.As the oxygen content increases,it first decreases from 65 K to 54 K and then rises to 76 K.With the increase of oxygen content in Zr₆₁Cu₂₅Al₁₂Ti₂ alloy,the formation and expansion of the shear band were inhibited,and the compression plasticity was gradually reduced.However,below the critical value of 780 ppm,the compression plasticity reduction is not significant,and the alloy can be considered as the critical value.The plasticity of the alloy is maintained as the oxygen content is increased below.When the oxygen content exceeds 1900 ppm,the compression plasticity of the material is almost completely lost due to the large amount of formation of the?₃ crystal phase.The increase of oxygen content makes the compressive strength of Zr₆₁Cu₂₅Al₁₂Ti₂ alloy increase,but it has little effect on the elastic deformation.The Weibull modulus m is used to characterize the variability of the data.The Zr₆₁Cu₂₅Al₁₂Ti₂ alloy has the highest strength reliability at an oxygen content of 360 ppm.Plasticity has lower reliability than strength,but the change in oxygen content has little effect on the reliability of plasticity.Compared to the two-parameter Weibull,the use of the three-parameter Weibull provides a more accurate BMGs reliability assessment.In addition,the concept of Failure-Free Stress?FFS?should be of significant engineering importance as it specifies the critical stress limits that safety engineering design should not exceed.Therefore,it is strongly recommended that the FFS of BMGs to be applied to load-bearing structures should be carefully evaluated.